Boring tool tracking/guiding system and method with unconstrained target location geometry

ABSTRACT

Tracking a boring tool is performed within an underground region using a locating signal. The boring tool is moved through the ground during a series of distance movements such that potential movement of the boring tool during any one of the distance movements is less than a maximum movement value. A current positional relationship is determined for a current one of the distance movements based on: a last-determined positional relationship established for an immediately preceding one of the distance movements, certain orientation parameters, the maximum movement value and the determined signal strength of the locating signal in the current positional relationship. Target coordinates are accepted and a target position, based on the target coordinates, is included as part of the current positional relationship. The position of the target is unconstrained with respect to system geometry. Steering command features are provided along with steering warnings.

BACKGROUND OF THE INVENTION

The present application is a continuation application of applicationSer. No. 11/247,300, filed on Oct. 11, 2005 now U.S. Pat. No. 7,084,636;which is a divisional application of application Ser. No. a 11/135,968,filed on May 24, 2005 and issued as U.S. Pat. No. 6,975,119 on Dec. 13,2005; which is a divisional of application Ser. No. 10/971,662, filed onOct. 22, 2004, and issued as U.S. Pat. No. 6,917,202 on Jul. 12, 2005;which is a divisional of application Ser. No. 10/792,476, filed on Mar.3, 2004, and issued as U.S. Pat. No. 6,856,135 on Feb. 15, 2005; whichis a divisional of application Ser. No. 10/001,854, filed on Nov. 20,2001, and issued as U.S. No. Pat. 6,727,704 on Apr. 27, 2004; thedisclosures of which are incorporated herein by reference.

The present invention relates generally to the field of tracking and/orguiding a boring tool to an underground location using anelectromagnetic locating signal and, more particularly, to a system andmethod which provides for guiding the boring tool to any selectedlocation within an underground region. The target location isunconstrained with respect to any system component geometricarrangements so long as the receiving position is within a receivingrange of the boring tool.

One early approach taken by the prior art in tracking a boring toolemploys accelerometer and magnetometer sensors in the boring tool.Information is sent to an above ground display through the use of acable to display pitch and yaw information. In one improvement, thepitch and yaw angles of the boring tool are integrated to estimate theposition of the boring tool. It should be appreciated that boring toolposition relative to a target is not available in this system. Moreover,accumulation of pitch and yaw measurement errors adversely influencesthe estimated boring tool position.

Another, more recent, approach taken in the prior art, with regard toguiding an in-ground boring tool, embodies a “homing” configuration. Insuch a configuration, the boring tool homes-in on a receiving positionat which a receiver is located. Homing configurations are generallyincapable of homing-in on anything other than the receiving positionitself. That is, the target of the boring tool is necessarily limited tothe position of the receiver. In one improvement, U.S. Pat. No.4,881,083 (hereinafter the '083 patent) describes a homing configurationwherein the boring tool homes-in on a vertically oriented line extendingthrough the receiver, in one embodiment, or homing in on the receiveritself, in another embodiment. In accordance with the former embodiment(see FIG. 1 of the '083 patent), the receiver is positionable above apit for purposes of drilling to some previously underground point on thevertical line below the previous surface of the ground. The system,however, does nothing with respect to monitoring the depth of the boringtool. The depth of the boring tool must be independently established orcontrolled for the boring tool to properly emerge in the pit. In thelatter embodiment (see FIG. 8 of the ('083 patent) and consistent withthe prior art in general, the system is incapable of doing any thingother than homing on the receiving position. That is, no target otherthan the receiving position is possible.

A marked improvement over the general state of the prior art isdescribed as one aspect of U.S. Pat. No. 6,250,402 (hereinafter the '402patent) which is co-assigned with the present application and which isincorporated herein by reference. In contrast with the prior art, the'402 patent provides for steering a boring tool to specified depthtarget locations that are directly below the receiver (see FIG. 9 of the'402 patent). As described at column 27, lines 18–20 of the '402 patent,however, even this technique is limited in that the target may not bepositioned beyond or in front of the receiver. It should also beappreciated that the target may not be positioned to the side (i.e.,laterally displaced) of the receiver.

The present invention serves to remove the foregoing constraints withrespect to the prior art while providing still further advantages, aswill be described.

SUMMARY OF THE INVENTION

As will be described in more detail hereinafter, there are disclosedherein apparatus and an associated method for tracking and/or guiding aboring tool to a selected underground location.

In one aspect of the present invention, a system is described fortracking a boring tool within an underground region. In this system, theboring tool is configured for transmitting a dipole locating signal andthe position of the boring tool is characterized, at least in part, bycertain orientation parameters. From a first position, the boring toolis moved to a second position during a time interval. The first positionforms part of a first positional relationship relative to a receivingposition. With the boring tool at the second position, a signal strengthof the locating signal is measured at the receiving position as well asthe certain orientation parameters of the boring tool. A maximummovement value for the boring tool is established such that anypotential movement of the boring tool over the time interval is lessthan the maximum movement value. Based on the first positionalrelationship, the certain orientation parameters, the maximum movementvalue and the determined signal strength of the locating signal at thesecond position, a second positional relationship is determinedincluding the boring tool at the second position relative to thereceiving position.

In another aspect of the present invention, target coordinates areobtained to which the boring tool is to be directed. In one feature, thetarget coordinates are specified by a user relative to the receivingposition. A target position is then determined relative to the boringtool.

In yet another aspect of the present invention, an intended path of theboring tool, extending between target and starting positions, may belonger than a dipole receiving range which defines a physical limit asto the potential distance between the boring tool and the locator, at orless than which limit the dipole locating signal is receivable by thelocator. In one feature, the locator may be positioned laterally offsetfrom the intended path. In another feature, a first position of theboring tool and a target location may be arranged to define the intendedpath as being approximately double the dipole receiving range.

In still another aspect of the present invention, steering commands aregenerated as part of a complete steering solution where desired pitchand yaw angles are specified for the boring tool at the target locationin addition to the target coordinates.

In a further aspect of the present invention, a system for tracking aboring tool within an underground region is described, in which systemthe boring tool is configured for transmitting a dipole locating signalaxially coincident with an elongation axis of the boring tool. Astarting positional relationship is determined including the boring tooland a receiving position at which the dipole locating signal is to bemonitored such that the receiving position is generally ahead of theboring tool. The boring tool is moved in a direction generally forwardthrough the ground during a series of distance movements such that eachdistance movement is is less than a maximum movement value. For eachdistance movement making up a first sequence in the series of distancemovements, at least measured values of the locating signal taken at thereceiving position are used to determine a forward distance from theboring tool to an orthogonal plane defined normal to the elongation axisand including the receiving position. When, for a particular one of thefirst sequence of distance movements, the forward distance is determinedto be less than the maximum movement value, the dipole locating signalis thereafter monitored during a second sequence in the series of thedistance movements in a predetermined way which detects a specific oneof the distance movements concluding the second sequence during whichthe boring tool crosses the plane.

In another aspect of the present invention, for each distance movementsin a third sequence of the series of distance movements, monitoring ofthe dipole locating signal continues in the predetermined way foranother crossing of the plane while a rearward distance is determinedfrom the boring tool to the plane now located behind the boring tool.When the rearward distance determined following one of the distancemovements concluding the third sequence is greater than the maximummovement value, for each distance movement making up a fourth sequenceof the series of distance movements, at least measured values of thelocating signal taken at the receiving position are used to confirm thatthe rearward distance is greater than the maximum movement value.

In an additional aspect of the present invention, a system is describedfor tracking a boring tool within an underground region, in which systemthe boring tool is configured for transmitting a dipole locating signalaxially coincident with an elongation axis of the boring tool. Astarting positional relationship is determined including the boring tooland a receiving position at which the dipole locating signal is to bemonitored. The boring tool is moved through the ground during a seriesof distance movements such that each distance movement of the boringtool is less than a maximum movement value. For each distance movement,a current positional relationship is determined for a current one of thedistance movements based on (i) a last-determined positionalrelationship established for an immediately preceding one of thedistance movements, (ii) the certain orientation parameters, (iii) themaximum movement value and (iv) the determined signal strength of thelocating signal in the current positional relationship. In one feature,target coordinates are accepted and a target position, based on thetarget coordinates, is included as part of the current positionalrelationship.

In a continuing aspect of the present invention, a system tracks aboring tool that is moved by a drill string within an undergroundregion. Movement of the boring tool is characterized by certainorientation parameters including pitch and yaw and the system isconfigured at least for establishing the pitch and yaw orientation ofthe boring tool. Initially, a first pitch orientation and a first yaworientation of the boring tool are determined corresponding to a firstposition of the boring tool. The boring tool is moved to a secondposition. A second pitch orientation and a second yaw orientation of theboring tool are determined for the second position as well as a distancebetween the first and second positions. Using the first and second pitchvalues, the first and second yaw values and the distance between thefirst and second positions, a curvature of the drill string isdetermined. In one feature, the first and second pitch values are usedto determine a pitch angle increment and the first and second yaw valuesare used to determine a yaw angle increment. Thereafter, the pitch angleincrement and the yaw angle increment are used, in combination, toestablish an angular deflection of the drill string for use indetermining the curvature of the drill string. In another feature, aratio of the angular deflection to the distance between the first andsecond positions is used to determine the curvature of the drill string.

In another aspect of the present invention, a system tracks a boringtool that is configured for transmitting a dipole locating signal withinan underground region where movement of the boring tool is characterizedby certain orientation parameters including pitch and yaw. The system isconfigured at least for establishing the pitch and yaw orientations ofthe boring tool. Means is provided for accepting a target location towhich the boring tool is to be guided including a target pitchorientation and a target roll orientation. Receiving means measures thelocating signal at a receiving position. Processing means then generatessteering commands for use in guiding the boring tool to the targetlocation using (i) measured values of the locating signal taken at thereceiving position by the receiving means, (ii) measurements of thepitch and yaw orientations of the boring tool, (iii) the target pitchorientation and (iv) the target yaw orientation. In one feature, theprocessing means is configured for generating the steering commands withthe target position at least laterally offset with respect to thereceiving position. In another feature, the processing means generatesthe steering commands by producing a horizontal steering command and avertical steering command in a mathematically coupled manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood by reference to the followingdetailed description taken in conjunction with the drawings brieflydescribed below.

FIG. 1 is a diagrammatic plan view of a boring tool locating/trackingsystem produced in accordance with the present invention showing thearrangement of a boring tool and above ground locator.

FIG. 2 is a diagrammatic elevational view of the system of FIG. 1, shownhere to illustrate further details with regard to the arrangement of thelocator and boring tool.

FIG. 3 is an enlarged diagrammatic view, in perspective, of the boringtool of FIGS. 1 and 2, shown here to illustrate a global coordinatesystem, a transmitter fixed coordinate system and several angular valuesrelated thereto as used by the present invention.

FIG. 4 is diagrammatic elevational end view of the boring tool of FIGS.1–3 showing the transmitter fixed coordinate system in relation to anumber of flux lines of the locating signal emitted by the boring tool.

FIG. 5 is another diagrammatic elevational end view of the boring toolof FIGS. 1–3 further showing an edge view of a flux plane used incharacterizing the locating signal in polar coordinates.

FIG. 6 is a diagrammatic elevational view of the boring tool, shown hereto illustrate a number of tracking regions used in a highly advantageousway by the present invention for empirically monitoring progress of theboring tool irrespective of certain ambiguities seen in the locatingsignal emitted from the boring tool.

FIG. 7 is a diagrammatic illustration of a display showing a possiblerepresentation of a positional relationship between the boring tool anda target position determined in accordance with the highly advantageoustracking technique of the present invention.

FIG. 8 is a diagrammatic illustration of another display illustratingsteering commands produced in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the figures wherein like components are indicated by likereference numbers throughout the various figures, attention isimmediately directed to the plan view of FIG. 1 which illustrates aboring tool locating and steering system generally indicated by thereference numeral 10. System 10 is positioned in a region 12 andincludes a boring tool 14 and a portable locator or receiver 16. Whilethe latter is illustrated in the form of a portable locator, it is to beunderstood that any suitable form of receiver may be employed such as,for example, a detector designed to be operated from a generally fixedposition. Such fixed position detectors are illustrated, for example, inthe '402 patent discussed previously. For purposes of this disclosure,boring tool 14 may be referred to interchangeably as a steering tool oras a transmitter. A drill string 18 is partially illustrated as a dashedline which extends to a drill rig that is not shown. While the drill rigmay be configured for moving the steering tool by means of the drillstring in a conventional manner, it is to be understood that portions ofsystem 10 such as, for example, processing arrangements and steeringapparatus are readily locatable at the drill rig. Such modifications andconfigurations have not been illustrated for purposes of brevity but arenonetheless considered as being within the capabilities of one havingordinary skill in the art in view of this overall disclosure.

Still referring to FIG. 1, boring tool 14 includes a mono-axial antenna(not shown) such as a dipole antenna oriented along an elongation axisof the boring tool and which is driven to emit a dipole magneticlocating signal 20 (only one flux line of which is partially shown). Asan example of a boring tool incorporating such a mono-axial antenna inits transmitter arrangement, see FIG. 9 of U.S. Pat. No. 5,155,442 andits associated description. This latter patent is co-assigned with thepresent application and hereby incorporated by reference. Inasmuch asdeterminations made by the present invention are based, at least inpart, on the orientation of the boring tool, the latter is equipped withtriaxial clusters of accelerometers and magnetometers configured tomeasure pitch, roll and yaw (azimuth) orientation angles of the boringtool along three orthogonally opposed axes. One such triaxialaccelerometer/magnetometer configuration forms part of a compositemagnetic signal detection arrangement described in U.S. Pat. No.6,191,585 which is commonly assigned with the present application and ishereby incorporated by reference. Transmission of these parameters tolocator 14 or to another location, such as the drill rig, is known inthe art. For example, data may be encoded on the locating signal itselffor transmission.

Considering locator 16, while desirable it is not an absolute necessityto configure the locator with a built-in magnetometer for ease ofdetermination of the direction in which the locator is pointed, as willbe further discussed. Moreover, locator 16 should include tilt sensorsand associated data processing equipment to rotate measured antennafluxes to level coordinates. Alternatively, the locator should beleveled or its tilt angles measured in a suitable manner. The locatorreceives the locating signal, as well as any encoded data, using atriaxial antenna cluster for reception along three orthogonally opposedaxes. One highly advantageous triaxial antenna cluster is described inU.S. Pat. No. 6,005,532 which is commonly assigned with the presentapplication and is incorporated herein by reference. As one component ofsystem 10, either locator 16 itself or a remote unit (not shown), shouldbe equipped with data processing capability sufficiently powerful tocompute steering parameters and/or display graphics.

Having described system 10 from a hardware standpoint, attention is nowdirected to operational use of the system. The applicable procedure fordetermining the reference direction 22 depends on whether or not locator16 features a magnetometer. If the locator is equipped with such adevice, the locator may be placed on the ground, pointed in a referencedirection 22, shown corresponding to the elongation axis of the locatorin FIG. 1. While shown as being parallel to the drilling direction, itis to be understood that this is not a requirement. The selection of thereference direction is as easy as aiming the locator away from the drillrig in what is generally thought to be the drilling direction. Further,this process is initiated with the locator ahead of the boring tool withrespect to what is thought to be the general drilling direction. Thislatter constraint is easily satisfied within the typical process ofperforming system setup prior to the actual start of drilling. It isnoted that the locator may be laterally offset from the actual forwarddirection of the boring tool, as illustrated. This procedure allows theuser to specify a very general reference direction. In instances wherethe receiver does not feature a magnetometer, the initial direction ofthe steering tool can be used to define the reference direction. Thepreferred approach is to place the steering tool on the ground ahead ofthe drill before drilling begins and to record its angle with respect tomagnetic north of the Earth thereby defining the reference direction.This procedure is expected to be more accurate than using the directionof the boring tool at drill begin where the close proximity of the drillstring might distort the flux lines emitted by the boring tool.

Referring to FIGS. 2 and 3 in conjunction with FIG. 1, system 10operates within a global coordinate system having its origin defined tobe at the center of the transmitter (i.e., the center of the antenna).That is, the global coordinate system origin corresponds to the originof dipole locating signal 20. A global x-coordinate axis, indicated asx, points in the reference direction is established during setup. Forconvenience, a number of variables are listed in Table 1 with anassociated description of each variable. FIG. 1 further illustrates aglobal y coordinate axis extending horizontally and orthogonal to the xaxis while FIG. 2 illustrates region 12 in elevation including a globalz coordinate axis extending vertically perpendicular to the global x,yplane. FIG. 3 is an enlarged elevational view of boring tool 14 showingselected axes which make up both global and transmitter fixedcoordinates, as will be further described.

TABLE 1 Variable Name Description of Variables x, y, z Coordinates of aglobal system with origin at the center of the transmitter, x points inthe reference direction of the transmitter, x, y are defined in a levelplane, and z is defined positive upward. x_(t), y_(t), z_(t) Transmitterfixed coordinates where x_(t) is along the transmitter axis, y_(t)normal to the transmitter axis, and z_(t) such that a right handedcoordinate system is formed. Note transmitter coordinates do not rotatewhen the transmitter is spinning about its axis but move when thetransmitter is pitched and yawed. For zero pitch and yaw coordinates x,y, z and x_(t), y_(t), z_(t) are identical. b_(x), b_(y), b_(z) Measuredcomponents of flux in global coordinates at the center of the receiverantenna cluster. Note fluxes are for unit transmitter dipole strength.x_(R), y_(R), z_(R) Receiver coordinates in the global system. Notethese are coordinates of the center of the antenna cluster. x_(T),y_(T), z_(T) Target coordinates in the global coordinate system. b_(x)_(T), b_(y) _(T), b_(z) _(T) Fluxes at the target in global coordinates.β Transmitter yaw angle defined in the global x, y plane. β_(T)Transmitter yaw angle at target, user specified. φ Transmitter pitchangle defined in a plane normal to the global x, y - plane, positive upas seen in FIG. 3 φ_(T) Transmitter pitch angle at the target, userspecified. δY, δZ Steering commands, used as position coordinates forthe steering indicator symbol seen in FIG. 8.

Continuing to refer to FIGS. 1–3, receiving coordinates in the globalsystem are determined by solving the known magnetic dipole equations inorder to develop a positional relationship between the receivingposition of the locator and the boring tool. This step requires the useof measured fluxes for unit transmitter dipole strength, transmitterpitch and yaw. Measured fluxes b_(x), b_(y), b_(z) are transformed fromglobal to transmitter fixed coordinates using:

$\begin{matrix}{\begin{Bmatrix}b_{x_{t}} \\b_{y_{t}} \\b_{z_{t}}\end{Bmatrix} = {T_{2}T_{1}\begin{Bmatrix}b_{x} \\b_{y} \\b_{z}\end{Bmatrix}\mspace{11mu}{with}}} & (1) \\{T_{1} = \begin{Bmatrix}{\cos\;\beta} & {\sin\;\beta} & 0 \\{{- \sin}\;\beta} & {\cos\;\beta} & 0 \\0 & 0 & 1\end{Bmatrix}} & (2) \\{T_{2} = \begin{Bmatrix}{\cos\;\phi} & 0 & {\sin\;\phi} \\0 & 1 & 0 \\{{- \sin}\;\phi} & 0 & {\cos\;\phi}\end{Bmatrix}} & (3)\end{matrix}$

It is appropriate at this juncture to note that global coordinatesdiffer from transmitter fixed coordinates only with respect to the pitchand yaw angles of the boring tool. That is, transformation from onecoordinate system to the other requires two rotations. If the boringtool is at zero pitch and yaw, the two coordinate systems coincideexactly. FIGS. 1 and 2 illustrate the transmitter fixed coordinate axesyawed (the x_(t), y_(t) plane rotated about the z axis) and pitched (thex_(t), z_(t) plane rotated about the y_(t) axis), respectively, whencompared to the global coordinate axes. In this regard, it is noted thatthe word “global” merely references an invariability of the globalcoordinate system over the entirety of the drilling region. In theexpressions of equations 1–3, T₁ and T₂ represent rotation matriceswherein T_(t) is associated with the yaw rotation and T₂ is associatedwith the pitch rotation. The remaining variables are as defined in Table1.

Turning now to FIGS. 4 and 5, the former is an end view of boring tool14 showing flux lines of dipole locating field 20 extending radiallyoutward from the boring tool. The latter figure is an end view of boringtool 14, looking forward from behind the boring tool, illustrating thetransmitter fixed coordinate axes relative to other parameters to bedescribed. The flux of the dipole locating signal is transformed to anξ,ζ plane defined including the elongation axis of the boring tool aswell as the center of the receiver antenna cluster and having an origincoincident with the origin of the dipole locating signal. That is, a ξaxis is coincident with the elongation axis of the boring tool and,likewise, the x_(t) axis while a ζ axis extends orthogonal to the ξ axisin a direction which positions locator 16, which is diagrammaticallyindicated as a point, in the ξ,ζ plane. This arrangement serves tosimplify calculation of locator coordinates since the flux-line patternof a magnetic dipole is axi-symmetric and, therefore, a total fluxvector measured by the receiver is contained in the ξ,ζ plane. Arotation angle σ is defined, as shown in FIG. 5, between the z_(t) andthe ζ axes. The component of intensity of the locating signal that isoriented along the ζ axis is indicated as b_(ζ). This latter fluxintensity is projected onto the y_(t) and z_(t) axes as components b_(y)_(t) and b_(z) _(t) , respectively.

Referring to FIG. 5, the rotation angle σ follows from:

$\begin{matrix}{{\tan\;\sigma} = \frac{- b_{y_{t}}}{b_{z_{t}}}} & (4)\end{matrix}$It is noted that equation 4 is not defined if b_(y) _(t) =b_(z) _(t) =0.There are 3 positions of the locator with respect to the boring tool forwhich this is the case, requiring a different approach to calculatinglocator coordinates. One such case arises when locator 16 is on thelocate line. In the other cases the boring tool is either pointing tothe center of locator 16 or away from it. In this regard, onecharacteristic of a dipole magnetic field is a locate line that isdefined on a level ground surface at zero transmitter pitch wherein themagnetic flux lines bisecting a plane orthogonal to the elongation axisof the boring tool transmitter and containing the origin of the dipolelocating signal are parallel to the elongation axis of the boring toolat the orthogonal plane as well as being horizontal relative to thelevel ground surface. Hence, passing the locate line during steering maymomentarily produce ambiguous results. Because the locate line is alwayscontained in the orthogonal plane to the axis of the transmitter, thelocate line, therefore, shifts in position on the ground surface withchanges in transmitter pitch. When the boring tool is pitched, the pointat which b_(y) _(t) =b_(z) _(t) =0 shifts is in direct proportion to thepitch.

Referring to FIG. 6 which is a view of the ξ,ζ plane taken normalthereto and FIG. 5, components of flux in the ξ,ζ plane are determinedas:b_(ξ=b) _(x) _(t) , and   (5)b_(ζ=b) _(z) _(t) cos σ−b_(y) _(t) sinσ  (6)

FIG. 6 further illustrates determination of the receiver coordinatesperformed in polar r, α coordinates in the ξ,ζ plane wherein a radius rextends from the origin to the position of locator/receiver 16 which isillustrated as a dot. It should be appreciated that this position is, infact, the center of the antenna array used to detect the locatingsignal. An angle α is formed between the ξ axis and r. Accordingly, thepolar coordinates are determined by:ξ_(R) =r cos α  (7)ζ_(R) =r sin α  (8)where radius r is obtained using:

$\begin{matrix}{\frac{1}{r^{3}} = {{{- \frac{1}{4}}b_{\xi}} + \sqrt{{\frac{9}{16}b_{\xi}^{2}} + {\frac{1}{2}b_{\zeta}^{2}}}}} & (9)\end{matrix}$

With regard to these determinations in the ξ,ζ plane, it is important tonote that the dipole field has fore and aft symmetry so that fluxesalone do not uniquely define angle α. Accordingly, the present inventionintroduces a highly advantageous technique for establishing anunambiguous position of the steering tool with respect to the receiver.This technique utilizes known information and, more specifically, tracksthe relative positional relationship between the boring tool and thelocator based on a “last-determined” positional relationship whichencompasses the most recent information available with respect to therelative positional relationship.

Referring again to FIGS. 5 and 6, the present invention employs anempirical tracking technique within an overall process for monitoringthe relative position between boring tool 14 and locator 16. Theempirical tracking technique of the present invention monitors thisrelative positional relationship by establishing three tracking regionsreferenced to a current position of the boring tool and its elongationaxis. Specifically, these tracking regions are indicated by the lettersF, A and R designated in FIG. 6. Region A is defined extending upwardlyfrom, but does not include the ξ axis and extends laterally betweenfirst and second tracking boundaries 30 and 32, respectively, each ofwhich is located at a distance “d” from the ζ axis oriented normal tothe ξ axis. Region A is further designated as A1 ahead of the boringtool up to boundary 32 and A2 behind the boring tool up to boundary 30.The forward direction of boring tool 14 is indicated by an arrowhead 34on the ξ axis. Specific considerations for establishing distance d willbe described at an appropriate point below.

It should be mentioned that the empirical tracking technique of thepresent invention has been developed under the constraint that thelocator position is above the boring tool in the ξ,ζ plane as viewed inFIG. 6 for all of the FAR tracking regions. This constraint, however,imposes no limitation on the actual positional relationship which mayexist between the boring tool and locator since angle σ, shown in FIG.5, may vary over a full 360°. Any apparent limitation imposed by the ξaxis boundaries of the FAR tracking regions is compensated for by thefull angular orientation capability of σ. In this regard, it is to beunderstood that the direction which appears as upward in FIG. 6 is, interms of actual directional orientation, unlimited as defined by σ.

With continuing reference to FIG. 6, tracking region F extends forwardfrom tracking boundary 32 while tracking region R extends to the rear ofboring tool 14 from first tracking boundary 30. Initially, thisempirical aspect of the tracking process of the invention relies on atleast a limited knowledge of the starting positional arrangement betweenthe boring tool and the locator. In particular, the initial position ofthe locator must be specified as ahead of or behind the boring tool.Within the context of initial setup, this requirement is easilysatisfied since, in most instances, the locator is readily stationedahead of the boring tool in the general direction of drilling prior toany actual drilling. Having established this initial positionalarrangement, system 10 automatically tracks the progress of boring tool14 relative to locator 16, as will be further described.

With regard to establishing distance d, it is first important tounderstand that the empirical tracking technique of the presentinvention monitors the relative positional relationship in anincremental fashion. That is, tracking proceeds by considering changesin the relative positional relationship over a series of distancemovements. Distance d is an empirical quantity chosen such that it isimpossible for the steering tool to move more than a distance d during asingle one of the distance movements. Several advantages arise in viewof these empirical constraints. First, the relative position of locator16 cannot move from tracking region F to tracking region R in onedistance movement (i.e., from one incremental position determination tothe next successive one). In fact, the relative movement must be fullywithin region A for at least one distance movement. Second, as theboring tool incrementally approaches the locator within distance d ofsecond tracking boundary 32, the locator will at least initially befound to be within tracking region A1 ahead of the boring tool (i.e.,ahead of the ζ axis).

Referring to Table 2 in conjunction with FIG. 6, determining a new orsubsequent relative positional relationship is performed at theconclusion of each distance movement in a predetermined way based inpart on the aforedescribed constrained incremental changes possible inthe positional relationship with respect to the FAR tracking regions.Another input is provided by the last-determined positionalrelationship. Specifically, the determination of any subsequentpositional relationship relies on which one of the regions of FIG. 6contained the receiving position at the time of the last-determinedpositional relationship. For this purpose, the last-determined positionis established as one of tracking region F (Table 2, Row 1), trackingregion R (Table 2, Row 5), tracking region A1 (Table 2, Row 2) ahead ofthe boring tool or tracking region A2 (Table 2, Row 4) behind the boringtool. The special case of the locator being on the ζ axis is shown inTable 2, Row 3. With regard to these various regions, it should beremembered that the regions move with the boring tool. Therefore, thelocator position appears to move through the regions relative to theboring tool even though it is the boring tool itself that is actuallymoving.

TABLE 2 Angular Row # Region Flux b_(ζ) Expression Equation 1 F b_(ζ) ≦0, b_(ζ) ≧ 0 α tan α = F₁ 2 A1 b_(ζ) > 0 α tan α = F₁ 3 ζ axis b_(ζ) = 0α = +90° — 4 A2 b_(ζ) < 0 α = γ + 180° tan γ = F₁ 5 R b_(ζ) ≦ 0, b_(ζ) ≧0 α = γ + 180° tan γ = F₁

The use of Table 2 will now be described in the context of the typicallocating situation in which the locator is initially ahead of the boringtool by more than distance d and then passes the locator along arelatively straight intended path that extends more than distance d pastthe locator, as orthogonally projected onto the intended path.

The expression F1, in Table 2 is given as:

$\begin{matrix}{F_{1} = \frac{( {{{- 3}b_{\xi}} + \sqrt{{9b_{\xi}^{2}} + {8b_{\zeta}^{2}}}} )\mspace{11mu}{sign}\mspace{11mu}( b_{\zeta} )}{2{b_{\zeta}}}} & (10)\end{matrix}$Accordingly, the locator is initially in the F tracking region such thatrow 1 of Table 2 is used wherein tan α=F₁. Radial distance r isdetermined using equation 9. Knowing the locator position in polarcoordinates, equations 7 and 8 may be used to determine the locatorcoordinates in the ξ,ζ plane. It should be appreciated that the boringtool may move toward the locator a number of times over a first sequenceof distance movements (each having a magnitude less than d) while stillremaining in tracking region F. For each of these movements which makeup the first sequence, the relative positional relationship isdetermined using Row 1 of Table 2. Prior to determining the subsequentpositional relationship associated with any distance movement, thelast-determined positional relationship must confirm that the locator isstill in region F. That is, the distance along the ξ axis must begreater than distance d.

With regard to “incremental” movement of the boring tool duringsuccessive ones of the distance movements, it is to be understood thatdeterminations of the tracking region in which the locator is positionedmay be made “on the fly” in a manner that is essentially invisible toboth the locator operator and drill rig operator. There is no need toactually incrementally move the boring tool corresponding to individualones of the distance movements.

Still referring to FIG. 6 and Table 2, whenever the distance along the ξaxis is determined to be less than distance d, the first sequence isterminated and a second sequence of distance movements is initiatedduring which the locator position progresses through region A1 withincremental movement of the boring tool. During the second sequence, itis important to monitor the flux of the locating signal in a way whichestablishes movement of the boring tool, in either of the fore and aftdirections, with respect to the position of the locator crossing the ζaxis. This condition may be referred to more simply as the boring tool“passing” the locator in either the forward or reverse directions. If,at any time, the distance along the ξ axis returns to a value that isgreater than d, the procedure of the first sequence is reentered.

The locating signal flux may be monitored in a number of different waysin order to detect the boring tool passing the locator. In one approach,the locating signal flux b_(ξ), measured along the ξ axis, will reach amaximum value at the exact point at which the boring tool passes thelocator in the described manner. This approach may be somewhat complex,however, when the movement of the boring tool is monitored in anincremental fashion since the flux will generally cross the maximumvalue at some point during an interval as opposed to at the precisemoment corresponding to the end of one interval and the beginning of asuccessive interval. Moreover, the maximum of b_(ξ) is not well defined(it is shallow) and, hence, quite difficult to locate even undercontinuous monitoring.

In another approach, the sign of the flux along the ζ axis may bemonitored with respect to passing the boring tool. This approach iscompatible with incremental movement monitoring since a comparison ofthe sign of the flux b_(ζ) need be performed so as to indicate theboring tool having passed the locator. That is, a change in the fluxsign indicates that the ζ axis was crossed at some point during theimmediately preceding distance movement. Further monitoring of the b_(ζ)flux will then indicate any re-crossing of the ζ axis as another changein the sign of the flux. In this way, the position of the locator ismonitored from one distance movement to the next until such time thatthe b_(ζ) flux changes sign. This event terminates the second sequenceof distance movements, as the boring tool passes the locator.

During the second sequence of distance movements, the relativepositional relationship is determined based on Row 2 of Table 2,indicating that b_(ζ) is greater than zero within region A1. It is notedthat the convention adopted here wherein b_(ζ)>0 in tracking region A1is employed for the purpose of descriptive clarity. Actual use of b_(ζ)requires only a comparative evaluation of the sign of this value whichchanges in sign upon the boring tool entering tracking region A2. Theposition of the locator relative to the boring tool is established inessentially the same manner as in tracking region F using tan α=F₁.Radial distance r is again determined using equation 9. Equations 7 and8 are then used to determine the locator coordinates in the ξ,ζ plane.

Referring to Row 3 of Table 2, in the potential, but rather unlikelyevent that b_(ζ)=0, the locator is positioned at a point along the ζaxis, α=+90°, which is a point on the locate line. The radius r can bedetermined from equation 9 and, consequently, the coordinates of thelocator will be known in the ξ,ζ plane. However, the locator position oncan not be obtained in the transmitter fixed coordinates since therotation angle σ is not defined for points on to locate line, asdiscussed earlier.

Row 4 of Table 2 corresponds to a third sequence of distance movementsduring which the boring tool incrementally moves the locator throughtracking region A2. Following any distance movement in the thirdsequence, the sign of the b_(ζ) flux is ascertained and compared to thesign of this flux determined for the last-determined positionalrelationship so as to confirm that the locator remains in trackingregion A2. Accordingly, per Table 2, the b_(ζ) flux sign correspondingto region A2 is less than zero where the flux sign b_(ζ) for region A1was considered as being positive. The coordinates of the locatorrelative to the boring tool are determined using an angle γ defined forcomputational purposes (also shown in Table 2), as:tan γ=F₁  (11)

Angle α is then determined as:α=γ+180°  (12)

Equation 9 is then used to determine radial distance r such that theposition of the locator is known in polar coordinates. Equations 7 and 8then give the position of the locator in the ξ,ζ plane. For eachdistance movement in the third sequence, the sign of flux b_(ζ) isverified to confirm that the locator remains in region A2. If the signchanges, the procedure of the second sequence is re-invoked. Generally,the boring tool continues moving forward such that the distance alongthe ξ axis surpasses distance d entering tracking region R. Upondetection of this condition, the third sequence is terminated and afourth sequence of distance movements is entered, as describedimmediately hereinafter.

During a fifth sequence of distance movements in which the locator is intracking region R, determinations are made in accordance with Row 5 ofTable 2. Specifically, a is determined in a manner consistent with thatused in region A2. Unlike region A2, however, monitoring the sign offlux b_(ζ) is not necessary from one distance movement to the next sincethe boring tool is incapable of moving by an amount that is sufficientto pass the boring tool in the reverse direction in a single distancemovement. Alternatively, tracking of the relative positionalrelationship with respect to the tracking regions proceeds by confirmingfrom one distance movement to the next that the distance along the ξaxis remains greater than d, the maximum movement value. In the eventthat the distance along the ξ axis is determined to be less than d, theprocedure in accordance with the fourth sequence of distance movementsis re-invoked.

The positional tracking technique of the present invention provides fortracking the relative positional relationship present between the boringtool and the locator as the boring tool progresses along someunderground path. While the movement of the boring tool was consideredabove as being along a generally straight path, it is to be understoodthat this constraint was imposed for descriptive purposes only.Operational use of this technique is in no way constrained to straightdrill paths, as will be appreciated by those skilled in the art. Atfirst blush, the advantages of the tracking technique of the presentinvention may not be fully apparent. In this regard, it is important tounderstand that a sweeping difference is provided over the prior art. Inparticular, the positional relationship is tracked irrespective of theboring tool passing the position of the locator. As discussed above,prior art techniques having been limited to directing the boring tool tothe receiver itself or to a location directly there below. The trackingtechnique of the present invention virtually sweeps away all constraintsas to a specified target position so long as the locator remains withinrange of the boring tool for purposes of receiving the dipole locatingsignal. With this being the only constraint, the target can be at anylocation including to the side of the locator and in front or behind thelocator. These advantages will become still more apparent in the contextof a discussion below wherein the tracking technique is employed insteering the boring tool to a specified target.

Using coordinates ξ_(R) and ζ_(R) of the locator determined fromequations 7 and 8, respectively, the locator receiving position isdetermined in transmitter fixed coordinates wherein:x_(t) _(R) =ξ_(R)  (13)y _(t) _(R) =−ζ_(R) sin σ  (14)z_(t) _(R) =ζ_(R) cos σ  (15 )where x_(t) _(R) , y_(t) _(R) , z_(t) _(R) represent thelocator/receiver position in transmitter fixed coordinates. Thesetransmitter fixed coordinates are transformed to global coordinatesusing:

$\begin{matrix}{\begin{Bmatrix}x_{R} \\y_{R} \\z_{R}\end{Bmatrix} = {T_{1}^{- 1}T_{2}^{- 1}\begin{Bmatrix}x_{t_{R}} \\y_{t_{R}} \\z_{t_{R}}\end{Bmatrix}}} & (16)\end{matrix}$in which x_(R), y_(R), z_(R) represent the locator/receiver position inglobal coordinates and where T₁ ⁻¹ and T₂ ⁻¹ are inverse rotationmatrices based on equations 2 and 3, respectively, given as:

$\begin{matrix}{T_{1}^{- 1} = \begin{Bmatrix}{\cos\;\beta} & {{- \sin}\;\beta} & 0 \\{\sin\;\beta} & {\cos\;\beta} & 0 \\0 & 0 & 1\end{Bmatrix}} & (17) \\{T_{2}^{- 1} = \begin{Bmatrix}{\cos\;\phi} & 0 & {{- \sin}\;\phi} \\0 & 1 & 0 \\{\sin\;\phi} & 0 & {\cos\;\phi}\end{Bmatrix}} & (18)\end{matrix}$

Having established the position of the locator in the global coordinatesystem, the position of a target may be established within the globalcoordinate system for display and steering purposes. It should beappreciated, as described above, that the target position is essentiallyunconstrained so long as the locating signal, with the boring tool atthe target position, will be receivable at the receiving position of thelocator. In order to facilitate ease of use from the viewpoint of asystem operator, the present invention provides for initialspecification of the target location relative to the locator. That is,the operator specifies the target location in terms of offsets from thelocator at its receiving position, for example, as Δx, Δy and Δz values.Such values are generally readily specifiable, for example, with only aminimal awareness of the actual orientation of the global coordinatesystem under the generally correct assumptions that the global x axisextends horizontally in the drilling direction, the global y axis ishorizontally orthogonal thereto and, of course, the global z axisextends vertically upward.

The relative receiver coordinates (Δx, Δy, Δz) are added to the targetcoordinates specified by the user to obtain the target position inglobal coordinates:x _(T) =Δx+x _(R)  (19)y _(T) =Δy+y _(R)  (20)z _(T) =Δz+z _(R)  (21)

FIG. 7 illustrates one possible appearance of a display 50, for example,presented on locator 16 including a target 52 centered in a pair ofcrosshairs 54. The display is presented as if the operator is looking inthe forward direction from behind boring tool 14 such that it appearsoffset from target 52 in the global y (left/right) and z ( up/down)directions. Exemplary y and z values are indicated as 6.3 feet and 5.5feet, respectively, at appropriate points adjacent to the crosshairs. Anexemplary forward distance to the boring tool is indicated in the upperleft hand corner of display 50 as “Target distance=22.8 ft”. Thus,distances to the target position are indicated along three axes. Withregard to steering boring tool 14 to target 52, the use of display 50 isintuitive. As illustrated, the boring tool must be steered up and to theright in order to approach the target. In using the display of FIG. 7,steering is executed by the user in order to move the boring tool to thetarget. The user in issuing steering commands, therefore, must besensitive to limitations of the drilling system such as, for example,the minimum bend radius of the drill string. Moreover, the user mustalso judge the feasibility of approaching the target at desired pitchand yaw angles based on the displayed offset values and current steeringtool pitch and yaw data.

Prior to considering the generation of steering commands, attention isdirected once again to FIG. 6 in order to consider the special cases inwhich locator 16 is either specified as the target or the boring toolmoves away from the locator along a straight trajectory.

In these cases b_(x) _(t) >0 and b_(y) _(t) =b_(z) _(t) =0, or accordingto equations 5 and 6 b_(ξ)>0 and b_(ζ)=0, so that the locator positionin transmitter fixed coordinates is written as:x _(t) _(R) =±(2/b _(x) _(t) )^(1/3)  (22)y_(t) _(r) =z_(t) _(r) =0  (23)The plus sign is used in Equation 22 if locator 16 is ahead of theboring tool in either regions F or A1, otherwise the minus sign applies.

As described above, the present invention provides remarkableflexibility with regard to the position of the target. In particular,the target position may be anywhere so long as the receiver is able topick up the dipole locating signal for tracking purposes upon the boringtool attaining the target position. It is also to be understood thatthis flexibility is accompanied by a further advantage with respect tothe path taken by the boring tool. Specifically, by arranging theinitial or first position of the boring tool at the start of drillingand the target location such that an intended path therebetween iswithin a dipole receiving range of the locator, the intended path of theboring tool may be seen to be longer than the dipole receiving range.The intended path, in this instance, is contemplated as being generallystraight. In fact, when the locator is stationed near the intended pathand spaced from the initial position of the boring tool by approximatelythe dipole receiving range along the drilling direction, the intendedpath is approximately twice the dipole receiving range. As compared tothe prior art, the present invention has, therefore, approximatelydoubled the potential length of the intended path, with accuracy ofmeasurement of fluxes emitted from a boring tool at the target generallyincreasing as the target is positioned closer to the locator, andaccuracy of measurement of the locating signal at any given pointgenerally increasing as the boring tool is closer to the locator.

Where the user specifies pitch, β_(T), and yaw, Ø_(T), at the targetposition, the present invention may provide further steering dataincluding steering commands. As mentioned above with regard to FIG. 7,target pitch and yaw data are not required input if the user is onlyinterested in boring tool position coordinates. In order to generatesteering commands, the target position is first determined intransmitter fixed coordinates using:

$\begin{matrix}{\begin{Bmatrix}x_{t_{T}} \\y_{t_{T}} \\z_{t_{T}}\end{Bmatrix} = {T_{2}T_{1}\begin{Bmatrix}x_{T} \\y_{T} \\z_{T}\end{Bmatrix}}} & (24)\end{matrix}$where x_(t) _(T) , y_(t) _(T) , z_(t) _(T) is the position of the targetin transmitter fixed coordinates and x_(T), y_(T), z_(T) is the positionof the target in global coordinates. T₁ and T₂ are rotation matrices, asdefined above. Locating signal fluxes at the target position and intransmitter fixed coordinates are derived from the dipole equations:

$\begin{matrix}{{b_{x_{t}}\text{❘}_{T}} = \frac{{3x_{t_{T}}^{2}} - r^{2}}{r^{5}}} & (25) \\{{b_{y_{t}}\text{❘}_{T}} = \frac{3x_{t_{T}}y_{t_{T}}}{r^{5}}} & (26) \\{{{b_{z_{t}}\text{❘}_{T}} = \frac{3x_{t_{T}}z_{t_{T}}}{r^{5}}},{and}} & (27) \\{r^{2} = {x_{T}^{2} + y_{T}^{2} + z_{T}^{2}}} & (28)\end{matrix}$where flux components at the target, b_(x) _(t) |_(T),b_(y) _(t) ,|_(T), b_(z) _(t) |_(T), in transmitter fixed coordinates are rotated toflux components at the target, b_(x) _(T) , b_(y) _(T) , b_(z) _(T) , inglobal coordinates using:

$\begin{matrix}{\begin{Bmatrix}b_{x_{T}} \\b_{y_{T}} \\b_{z_{T}}\end{Bmatrix} = {T_{1}^{- 1}T_{2}^{- 1}\begin{Bmatrix}{b_{x_{t}}\text{❘}_{T}} \\{b_{y_{t}}\text{❘}_{T}} \\{b_{z_{t}}\text{❘}_{T}}\end{Bmatrix}}} & (29)\end{matrix}$

Referring to FIG. 8, steering commands are produced based on userspecified pitch, β_(T), and yaw, φ_(T), at the target position using:

$\begin{matrix}{{\delta\; Y} = {{{- \tan}\;\beta_{T}} + \frac{b_{y_{T}}}{b_{x_{T}}}}} & (30) \\{{\delta\; Z} = {{\tan\;\phi_{T}} - \frac{b_{z_{T}}}{b_{x_{T}}}}} & (31)\end{matrix}$

If δY>0, steering to the left is required whereas δY<0 requires steeringto the right. If δZ>0, downward steering is required whereas δZ<0requires upward steering. Such steering commands may be displayed to anoperator or, alternatively, used by an automated steering system.Irrespective of how the commands are used, the generated commands may beproduced to accommodate various system limitations including but notlimited to drill string minimum bend radius. Steering commands may bedisplayed, for example, as illustrated by FIG. 8 including a steeringindicator 60 shown offset from target 52 which indicates that steeringdownward and to the left is required. The axes related to the δY and δZsteering commands are indicated adjacent to crosshairs 54 for reference.

Hence, where pitch, β_(T), and yaw, φ_(T), at the target position arespecified by the user, the present invention provides a completesteering solution. This solution is facilitated in cooperation with thehighly advantageous, empirically based tracking technique of the presentinvention wherein the relative positional relationship between theboring tool and locator is monitored in a way which permits thespecification of target positions anywhere within the drilling region.The primary limitation as to target position is that the receiver mustbe capable of receiving the locating signal when transmitted by theboring tool from the target position.

It should be understood that the steering commands generated by thepresent invention are determined in a mathematically coupled manner.That is, no assumptions are necessary with regard to δY (horizontal)steering in order to determine the δZ (vertical) steering command andvice versa. While the steering commands determined by the technique ofthe '402 patent remain advantageous at least for the reason that amagnetometer is not required in the boring tool, its steering commandsare determined in a mathematically uncoupled manner. Specifically, whencalculating the left/right steering command, it is assumed that theboring tool is vertically aimed (i.e., pitched) at the target.Similarly, when calculating the up/down steering command, it is assumedthat the boring tool is horizontally aimed (i.e., yawed) directly towardthe target.

When drilling the steering tool to a specified target, pitch and yaw aremeasured along the drill path and the distance from the steering tool tothe receiver is calculated as described. As will be seen, thisinformation can be used to warn the driller of an over-steeringsituation that could cause drill rod and other equipment damage.

The approach is to repeatedly calculate changes of rod deflection angleand rod length during drilling. The ratio of these two parametersrepresents rod curvature that is compared with a specified thresholdvalue considered sufficiently safe for the drill rod. The driller willbe warned of imminent over-steering if the computed rod curvatureexceeds the specified safe value. Other over-steering indicators such asrod-bending radius, defined as the inverse of curvature, or roddeflection angle can be used instead of curvature.

Having measured pitch and yaw at two neighboring steering tool positionsalong the drill path, labeled i-1 and i with i indicating the presentposition, pitch and yaw angle increments are calculated from:Δφ=φ_(i)−φ_(i-1)  (32)Δβ=β_(i)−β_(i-1)  (33)

Assuming moderately small pitch and yaw changes, a corresponding totalrod deflection angle is obtained from:Δμ=√{square root over ((Δφ)²+(Δβ)²)}{square root over((Δφ)²+(Δβ)²)}  (34)

Since the receiver position has already been established in globalcoordinates (x_(R), y_(R), z_(R)), rod length increments betweenpositions i-1 and i are determined using:Δs=√{square root over ((x _(R) _(i) −x _(R) _(i-1) )²+(y _(R) _(i) −y_(R) _(i-1) )²+(z _(R) _(i) −z _(R) _(i-1) )²)}{square root over ((x_(R) _(i) −x _(R) _(i-1) )²+(y _(R) _(i) −y _(R) _(i-1) )²+(z _(R) _(i)−z _(R) _(i-1) )²)}{square root over ((x _(R) _(i) −x _(R) _(i-1) )²+(y_(R) _(i) −y _(R) _(i-1) )²+(z _(R) _(i) −z _(R) _(i-1) )²)}  (35)

Assuming that the total rod deflection angle is given in radians, rodcurvature becomes:

$\begin{matrix}{\kappa = \frac{\Delta\mu}{\Delta\; s}} & (36)\end{matrix}$

A safe maximum value for curvature is obtained from:

$\begin{matrix}{\kappa_{\max} = {F\frac{1}{R_{\min}}}} & (38)\end{matrix}$

Here, R_(min) is the minimum recommended rod bend radius for the drillrod in use. The factor F is less than or equal to unity and representsan additional safety factor chosen by the driller. The driller will bewarned of over-steering if κ>κ_(max).

Several variations of this procedure can be implemented, all of whichare considered as being within the capability of one having ordinaryskill in the art in view of this overall disclosure. For instance, onecould calculate separate rod curvatures from pitch and yaw angle changesand compare the larger of the two values with κ_(max). In anothervariation, one could monitor rod bending radius R=1/κ and warn thedriller if R<R_(min). Furthermore, one could estimate the total rodbending angle for the whole length l_(rod) of the drill rod using:

$\begin{matrix}{{\Delta\mu}_{rod} = {\frac{l_{rod}}{\Delta\; s}{\Delta\mu}}} & (39)\end{matrix}$and issue a warning if Δμ_(rod) exceeds a specified maximum total rodbending angle. This warning may be provided on any display screenavailable in the system such as, for example, on locator 16 and/or in anaudible form.

Inasmuch as the arrangements and associated methods disclosed herein maybe provided in a variety of different configurations and modified in anunlimited number of different ways, it should be understood that thepresent invention may be embodied in many other specific forms withoutdeparting from the spirit of scope of the invention. Therefore, thepresent examples and methods are to be considered as illustrative andnot restrictive, and the invention is not to be limited to the detailsgiven herein, but may be modified within the scope of the appendedclaims.

1. In a system for tracking a boring tool within an underground regionusing a portable locator, in which system the boring tool is configuredfor transmitting a dipole locating signal and where the position of theboring tool is characterized, at least in part, by certain orientationparameters which are transmitted from the boring tool, a methodcomprising: from a first position, moving the boring tool to a secondposition during a time interval, said first position forming part of afirst positional relationship relative to the portable locator at alocator position; with the boring tool at the second position, measuringa signal strength of the locating signal with the portable locator andreceiving said certain orientation parameters from the boring tool withthe portable locator; establishing a maximum movement value for theboring tool such that any potential movement of the boring tool over thetime interval is less than the maximum movement value and saving themaximum movement value in the portable locator; and based on the firstpositional relationship, said certain orientation parameters, themaximum movement value and the determined signal strength of thelocating signal as received by the portable locator with the boring toolat the second position, configuring the portable locator for determininga second positional relationship including the boring tool at the secondposition relative to the portable locator at the locator position. 2.The method of claim 1 wherein said certain orientation parametersinclude yaw of the boring tool in said region.
 3. The method of claim 1wherein said certain orientation parameters include pitch of the boringtool in said region.
 4. The method of claim 1 wherein the boring tooldefines an elongation axis and said method includes determining a firstlateral distance, as part of the first positional relationship, measuredalong the elongation axis from the boring tool to an orthogonal planedefined as (i) including the locator position and (ii) intersecting theelongation axis normal thereto.
 5. The method of claim 4 wherein saidlocator is configured for determining the second positionalrelationship, at least in part, by comparing the first lateral distanceto the maximum movement value.
 6. The method of claim 5 whereincomparing establishes that the first lateral distance is more than saidmaximum movement value and the first positional relationship furtherestablishes that the locator position is ahead of the boring tool withrespect to said orthogonal plane.
 7. The method of claim 6 wherein thesecond positional relationship is determined, at least in part, using anangle α defined between the elongation axis of the boring tool and aline extending from the boring tool to the portable locator at thelocator position, said method including determining α using theexpression:${\tan\;\alpha} = \frac{( {{{- 3}b_{\xi}} + \sqrt{{9b_{\xi}^{2}} + {8b_{\zeta}^{2}}}} )\mspace{11mu}\sin\mspace{11mu}( b_{\zeta} )}{2{b_{\zeta}}}$where an orthogonal pair of axes ξ and ζ define an axial plane includingthe elongation axis of the boring tool and including the locatorposition such that ξ is coincident with the elongation axis of theboring tool and ζ is normal thereto in said axial plane and where b_(ξ)and b_(ζ) are components of the dipole locating field along the ξ and ζaxes, respectively.
 8. The method of claim 6 wherein the secondpositional relationship is determined, at least in part, based on aradial distance, r, between the second position of the boring tool andthe locator position established using the expression:$\frac{1}{r^{3}} = {{{- \frac{1}{4}}b_{\xi}} + \sqrt{{\frac{9}{16}b_{\xi}^{2}} + {\frac{1}{2}b_{\zeta}^{2}}}}$where an orthogonal pair of axes ξ and ζ define an axial plane includingthe elongation axis of the boring tool and the locator position suchthat ξ is coincident with the elongation axis of the boring tool and ζis normal thereto in said axial plane and where b_(ξ) and b_(ζ) arecomponents of the dipole locating field along the ξ and ζ axes,respectively.
 9. The method of claim 5 wherein comparing establishesthat the first lateral distance is less than said maximum movement valueand that the locator position is ahead of the boring tool, in the firstpositional relationship, when projected orthogonally onto the elongationaxis of the boring tool.
 10. In a system for tracking a boring toolwithin an underground region, in which system the boring tool isconfigured for transmitting a dipole locating signal and where theposition of the boring tool is characterized, at least in part, bycertain orientation parameters which are transmitted from the boringtool, a locator comprising: a receiver for measuring a signal strengthof the locating signal at a receiving position and for receiving saidcertain orientation parameters of the boring tool after moving theboring tool during a time interval from a first position, forming partof a first positional relationship relative to the receiving position,to a second position, where the boring tool is subject to a maximummovement value such that any potential movement of the boring tool overthe time interval is less than the maximum movement value; and aprocessor for determining a second positional relationship of the boringtool at the second position relative to the receiving position based onthe first positional relationship, said certain orientation parameters,the maximum movement value and the determined signal strength of thelocating signal at the second position.
 11. The locator of claim 10wherein said processor is configured for using yaw of the boring tool asone of said certain orientation parameters.
 12. The locator of claim 10wherein said processor is configured for using pitch of the boring toolas one of said certain orientation parameters.
 13. The locator of claim10 wherein the boring tool defines an elongation axis and said processoris configured for using a first lateral distance determined as part ofthe first positional relationship and measured along the elongation axisfrom the boring tool to an orthogonal plane defined as (i) including thereceiving position and (ii) intersecting the elongation axis normalthereto.
 14. The locator of claim 13 wherein said processor determinesthe second positional relationship, at least in part, by comparing thefirst lateral distance to the maximum movement value.
 15. The locator ofclaim 13 wherein said processor is configured for establishing when thefirst lateral distance is more than said maximum movement value wherethe first positional relationship places the receiving position ahead ofthe boring tool with respect to said orthogonal plane.
 16. The locatorof claim 15 wherein said processor is configured for determining thesecond positional relationship, at least in part, using an angle αdefined between the elongation axis of the boring tool and a lineextending from the boring tool to the locator using the angle α definedby the expression:${\tan\;\alpha} = \frac{( {{{- 3}b_{\xi}} + \sqrt{{9b_{\xi}^{2}} + {8b_{\zeta}^{2}}}} )\mspace{11mu}\sin\mspace{11mu}( b_{\zeta} )}{2{b_{\zeta}}}$where an orthogonal pair of axes ξ and ζ define an axial plane includingthe elongation axis of the boring tool and including the receivingposition such that ξ is coincident with the elongation axis of theboring tool and ζ is normal thereto in said axial plane and where b_(ξ)and b_(ζ) are components of the dipole locating field along the ξ and ζaxes, respectively.
 17. The locator of claim 15 wherein said processoris configured for determining the second positional relationship based,at least in part, on a radial distance, r, between the second positionof the boring tool and the receiving position using the expression:$\frac{1}{r^{3}} = {{{- \frac{1}{4}}b_{\xi}} + \sqrt{{\frac{9}{16}b_{\xi}^{2}} + {\frac{1}{2}b_{\zeta}^{2}}}}$where an orthogonal pair of axes ξ and ζ define an axial plane includingthe elongation axis of the boring tool and the receiving position suchthat ξ is coincident with the elongation axis of the boring tool and ζis normal thereto in said axial plane and where b_(ξ) and b_(ζ) arecomponents of the dipole locating field along the ξ and ζ axes,respectively.
 18. The locator of claim 14 wherein said processor isconfigured for establishing when the first lateral distance is less thansaid maximum movement value and where the first positional relationshipplaces the receiving position ahead of the boring tool, when projectedorthogonally onto the elongation axis of the boring tool.
 19. Thelocator of claim 18 where an axial plane is defined by the elongationaxis of the boring tool and including the receiving position andprocessor monitors one or more flux components of the dipole locatingsignal in said axial plane in a way which identifies the boring toolhaving passed the receiving position with respect to an orthogonal lineextending through the receiving position orthogonal to the elongationaxis of the boring tool as a part of the second positional relationship.20. In a system for tracking a boring tool that is configured fortransmitting a dipole locating signal within an underground region wheremovement of the boring tool is characterized by certain orientationparameters including pitch and yaw and which system is configured atleast for establishing the pitch and yaw orientations of the boringtool, a locator comprising: a user input that is configured foraccepting a target location to which the boring tool is to be guidedincluding a target pitch orientation and a target roll orientation; areceiver for measuring the locating signal at a receiving position ofthe locator; and a processor that is configured for generating steeringcommands for use in guiding the boring tool to the target location usingmeasured values of the locating signal taken at the receiving positionby said receiver, measurements of the pitch and yaw orientations of theboring tool, the target pitch orientation and the target yaworientation.